A well known clip-type terminal includes a flat piece of metal having an integrally formed, resilient, bifurcated portion providing one or more conductor-receiving slots. An insulated conductor is forced into the slot which is formed between opposing faces of the furcations or beams as they are often called and which is of a width that is considerably less that the diameter of the conductive element of the insulated conductor. See U.S. Pat. No. 3,112,147 which issued on Nov. 26, 1963 in the names of W. Pferd et al.
The insertion of the conductor into the slot results in a penetration of the insulation so that electrical contact is achieved between the conductor and the surfaces that define the slot. In some kinds of these terminals, the penetration is achieved by the insulation being crushed, while in others, it is achieved by the insulation being sliced by specially formed entrance portions of the slots.
Typically, a plurality of these terminals are mounted in apertures in a plastic block to form a connector. See for example, U.S. Pat. No. 3,234,498 which issued on Feb. 8, 1966 in the name of A. Logan. Such a terminal block and slotted insulation penetrating terminals are also shown in U.S. Pat. No. 3,836,942, for example. For use in some equipment, the terminals are formed with wire-wrapping tangs which depend from a lower surface of the block to facilitate the connection of additional conductors.
Some applications of these kinds of connectors require that more than one conductor be connected to the same terminal. In prior art terminals of this type which are adapted to receive more than one conductor, a bifurcated portion generally has been provided for each conductor with all pairs of furcations depending from a single strip of metal. Prior art connectors of this type include those in which two single slot terminals are overlapped with the overlapping portions being welded together.
In the use of multi-conductor clip terminals, the most common demand is for a two conductor terminal. Considerable space could be saved if a two conductor terminal could be made with three furcations or beams-one center and two side--thereby providing two slots with the middle beam being common to both slots. Such a terminal is shown in U.S. Pat. No. 3,605,071.
Besides the accommodation of plural conductors, the insertion of the conductors into the slots between the beams presents a problem. The construction of slotted insulation-penetrating terminals is such that considerable force is required to insert a conductor into one of its slots, with the result that a special insertion tool is usually provided. The tool has end surfaces which engage the insulated conductor at a point immediately adjacent to the side surfaces of the beams so that the conductor can be forced into the slot, thus spreading the beams. In the single conductor slotted terminal, it has been found that both beams are flexed an equal amount.
The characteristic of a slotted beam type terminal, whether of the insulation crushing type or the insulation slicing type, is that the contact force developed by the beams must be sufficient to effect the desired crushing or slicing of the insulation, but at the same time, not so great as to pinch off the conductor or to materially weaken the same by nicking. It is also desirable to design a terminal so that it will accommodate several conductor gauge sizes. With the larger size conductor, there is a greater deflection of the beams, and therefore a greater force is exerted on the conductor. This in itself is not particularly objectionable since the larger diameter conductors are better able to resist the pinching-off effect, but this tends to limit the ability of the terminal to accommodate a plurality of adjacent gauge size conductors.
In a two slot terminal having a common center beam and two lateral beams, both lateral beams react against the insertion of a first conductor. Thus, the insertion of the second conductor ordinarily requires a relatively greater force than that for the insertion of the first conductor due to the fact that one lateral beam is already stressed to an extent corresponding to its deflection. Therefore, the force ordinarily exerted by the clip beams on the second conductor might be sufficiently great to pinch off the conductive element of the conductor. In other words, the range of forces encountered in prior art two conductor, clip-type terminals is greater than those encountered in the design for a single conductor clip type terminal.
The clip type terminal of the above-identified U.S. Pat. No. 3,605,071 relies on relative stiffnesses as between the center beam and the two outer beams to avoid damage to the conductors while providing a trifurcated terminal. This arrangement attempts to restrict deflection of the outer beam particularly since the terminal establishes electrical engagement with an insulated conductor by crushing the insulation.
Arrangements for mounting a plurality of clip-type terminals in a molded plastic terminal block such as that shown in U.S. Pat. No. 3,394,454 and in U.S. Pat. No. 4,084,877 are well known. For example, in one mounting arrangement, each terminal is formed with a shoulder having an opening therein. When a terminal of this type is inserted into an aperture in a block, a protuberance in the aperture is depressed by a lower part of the shoulder. After the terminal passes a narrow part of the aperture, the protuberance returns to its original configuration and protrudes into the aperture thereby locking the terminal in the block.
Another problem in these kinds of arrangements relates to the density of the terminals in the block. Blocks which have been made available with the welded, overlapping terminal arrangement described hereinbefore have a relatively high density. It is desirable to be able to maintain that density without the necessity of welding together terminals and yet have a terminal which is capable of establishing electrical contact with a conductor without damaging the conductor. This presents a problem in that the furcations of the terminal must, within dimensional constraints, be capable of applying enough pressure to the conductor to displace the insulation yet be flexible enough so as not to damage the conductive portion of the insulated conductor.
What is needed and what is not provided by the prior art is a trifurcated beam type terminal which has provisions for isolating the deflection of one portion from the other. While this general configuration is available in the art, there does not seem to be one available, other than those that involve complex designs relating to relative stiffness, which electrically engages conductors without damaging them.